The invention relates to a method for manufacturing a nonaqueous cell employing an anode, a cathode comprising an active cathode material and an organic electrolyte. The method involves the direct addition of a beta-aminoenone, such as 4-amino-3-penten-2-one, to the electrolyte to aid in reducing any undesirably high initial open circuit voltage such as that normally observed with cathodes such as FeS2.
The development of high energy cell systems requires the compatibility of an electrolyte possessing desirable electrochemical properties with highly active anode materials, such as lithium, calcium, sodium and the like, and the efficient use of high energy density cathode materials. Such suitable high energy density cathode materials includes iron sulfides such as FeS2 and FeS, carbon flourides such as CFx, metal oxides such as V2O5, WO3, MoO3, lead oxides such as Pb3O4, PbO2 and PbO, cobalt oxides such as Co3O4, manganese oxides such as MnO2, In2S3, NiS, metal chromates such as Ag2CrO4, metal phosphates such as Ag3PO4, LiCoO2, LiMn2O4, Bi2O3, CuO and Cu2O and metal sulfates such as CuSO4. The use of aqueous electrolytes is precluded in these systems since the anode materials are sufficiently active to react with water chemically. Therefore, in order to realize the high energy density obtainable through use of these highly reactive anodes and high energy density cathodes, it is necessary to use a nonaqueous electrolyte system.
Many cell or battery applications, particularly in transistorized devices, such as hearing aids, watches, calculators, and the like, require a substantially unipotential discharge source for proper operation. However, it has been found that in many nonaqueous cells employing positive active materials, which include conductive additives such as graphite and/or carbon, the cell upon initially being discharged, exhibits a high voltage whereupon the cell then proceeds to reach its lower operating discharge voltage level only after a certain time period has elapsed. The time period for the cell to reach its intended operating discharge voltage level usually depends on the discharge rate through the load and thus, depending on the apparatus it is to power, could result in a period extending up to several hours or even days. This phenomenon has serious drawbacks when a cell is intended to be used in electronic devices requiring a substantially unipotential discharge source for proper operation. In some of these electronic devices, any initial voltage peak substantially exceeding the intended operating voltage for the device could result in serious damage to the electronic components of the device.
One approach to protect devices from batteries exhibiting high voltages prior to leveling off to their desired operating voltage level is to add additional electronic circuit components to protect the main operating components of the device. However, this not only adds to the expense of the device but also would result in enlarging the device to accommodate the protective circuitry. Larger devices run counter to the current emphasis placed on miniaturization, where it has become necessary for the battery industry to design smaller and smaller electrochemically powered cells.
Another approach designed to reduce an initially high and potentially disadvantageous voltage is to subject such cells to a pre-discharge regimen prior to initial use by an end user. But such pre-discharge regimens are time consuming and costly, and reduce the capacity of the cell. Therefore, it is desirable to reduce or eliminate any required pre-discharge.
It has been suggested in U.S. Pat. No. 4,489,144 that the addition of an isoxazole derivative, such as 3,5-dimethylisoxazole, to the electrolyte may compensate for or eliminate this initial high voltage during discharge of nonaqueous cells. It was believed that the isoxazole derivative reacted with unwanted species that presumably caused the initial high voltage by reducing these species. The entire disclosure of U.S. Pat. No. 4,489,144 is hereby incorporated by reference as if fully rewritten herein.
It has now been determined that a favorable reduction in initial open circuit voltage in a nonaqueous cell can be achieved by the addition of a beta-aminoenone to the electrolyte. Accordingly, it is an object of the within invention to provide a method for manufacturing a cell comprising a highly active anode such as lithium, a cathode comprising an active material such as FeS2, and a nonaqueous electrolyte comprising a beta-aminoenone such as 4-amino-3-penten-2-one.